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NMPi Future Climate Change Data Layers

Scottish Marine and Freshwater Science Vol 8 No 11

This report has been prepared to accompany the UK Climate Projections 2009 (UK CP09) layers added to ‘Marine Scotland MAPS NMPi'. NMPi is Marine Scotland’s on-line portal to provide spatial information and data to support national and regional marine planning and the state of the sea assessments required to support national and regional planning. This report briefly summarises the climate change data layers selected. A variety of time baselines are used in the climate change future projections (although all are generally for about 100 years in the future). Unfortunately the different time periods reflect how the source information was published, and this cannot be rectified in this report. Users can convert changes over the period published here to relative change per year, or per decade, and then estimate the size of changes for any specific year of their interest. When multiple emission scenarios have been used to give a range of future climate variable possibilities, the 50% probability solution has been used. For projections when only one emissions scenario is available, a medium emissions scenario of future societal change has been used in this report, although other emissions scenarios are available in the information sources listed.

Storminess: Currently there is no clear understanding of the future of storminess (i.e. storm intensity and frequency) over Scottish seas. UKCP09 makes no projections as to whether storminess will increase or decrease in the future. Different models predict different outcomes. Hence there is no NMPi Data Layer on Storminess. Winds: The models used in the UKCP09 project suggested that by 2080 there may be a slight decrease in winds over Scottish seas, by about 3%. There are small chances that this decrease could be double, or winds could increase by about 3%. These changes are small compared to natural variability, and regional differences across Scottish seas are not clearly evident, hence no NMPi Data Layer is presented for wind. Rainfall: The central estimate projections for the 2080s, using the medium emissions scenario as the most likely outcome of climate change, indicates that over Scotland summers will become up to 20% drier, and winters 20% wetter. Overall, the central estimate is for the annual average rainfall to be about 10% less in the 2080s. There are some regional differences, hence NMPi data layers for rainfall (precipitation) are presented. Air Temperature: For winter air temperatures, for the medium emissions scenario, the central estimate (50% probability) is for air temperatures to increase by between 1.1 and 2.4ºC by the 2080s. Increases are projected to be greater on the east coast than on the west coast. Increases are very unlikely to be greater than 4ºC, but also very unlikely to be less than 0.5 ºC. Very similar values are projected for summer air temperature increases. As there is some regional differences in the projections, NMPi data layers are presented for air temperature. Relative Sea Level: Currently it is estimated that the average sea level around the UK has risen at a rate of about 1 mm per year over the past century5 (if this rate of increase carried on to the year 2095, sea level around the UK will increase by about 86 cm). To help contingency planning in the UK, a prediction has been given of a “low probability, high impact” relative sea level rise, i.e. a “worst case” scenario. This prediction does not have any regional variation, and hence is not presented in the form of an NMPi Data Layer. It states that the sea level around our coast will rise by between 93 cm and 190 cm by 2095. These levels depend on worst case ice melting around the globe. For the medium emissions scenario, the least predicted rise in relative sea level occurs in the Clyde to Skye coastal waters, as well as the inner Firth of Forth and Moray Firth, with predicted rises of about 30 cm by 2095. The remainder of mainland Scottish coasts experience approximately 35 cm rise over the same period, while the Hebrides and Orkney experience a rise of 40 cm. The greatest predicted relative sea level rise by 2095 occurs in Shetland, with a rise of about 50 cm by 2095. An NMPi data layer for relative sea level rise is presented. Storm Surges: As described above, the current estimates of future climates do not suggest storminess will increase significantly over Scotland. Hence the predictions of increases in storm surge heights over the next 100 years is small. For most of Scotland the increases in extreme storm surges with return periods of 2, 10, 20 and 50 years are between about 1 and 3 cm by 2095. There is some regional variation, and hence an NMPi Data Layer for the increase in storm surge height is presented. Extreme Water Levels: Currently, the highest storm surge that may occur in a 50-year period raises the sea surface by between 90 and 180 cm. The effect is least on the east coast and in Shetland, and greatest on the west coast. The central estimate predicts that by 2095, these extreme water level events will have changed very little. However, the worst case projections suggest that the 50-year return extreme water levels will have risen to between 300 and 500 cm, again with the highest levels on the west coast, and lowest on the east. As there is some regional variation, NMPi data layers are presented for extreme water levels. Waves: Climate change projections suggest that by 2085, significant wave heights north of Scotland will decrease by about 30 cm in the winter while they will slightly increase around the southern UK. The other seasons have different patterns of change, although changes are quite small. Four NMPi data layers are given, each one showing the change in wave height for a different season. Hydrography – Temperature: By 2085, sea surface temperatures around Scotland are projected to be between 2 and 2.5ºC warmer. Further south around the UK sea surface temperatures may rise even more, by up to 3.5 or 4ºC. An exception occurs in summer, when surface temperatures north and west of Scotland may be only 1ºC warmer. The autumn seems to be when most warming will be evident.